The data used in this study involved the age of onset of disabling and/or severe (D/S) headache. Subjects were identified from a survey of a midwest non-clinical population which was conducted by the University of Kansas Department of Neurology. A mathematical procedure was derived to estimate the incidence rate and the age-specific incidence rates of D/S headache in that population. The validity of these estimates was examined in conjunction with the data on prevalence and on length of illness of headache existing in the published medical literature, and the relationship among these epidemiological indices. A report of this study is in preparation.